1. Technical Field
The present invention relates to a fixture structure configured so as to separate and reuse a micro-seismic sensor insertedly installed in a borehole.
2. Description of the Related Art
In order to effectively study and prepare for a micro-seismic tremor, it is necessary to accurately sense micro-seismic event at the time of generation of the micro-seismic event and rapidly transmit the observed micro-seismic event data to a data analyzing center.
A micro-seismic sensor is mainly configured of a micro-seismic motion sensor and a recorder, wherein the micro-seismic motion sensor is classified into a speed meter for measuring a motion speed of a ground and an accelerometer for measuring force of motion.
The speed meter is classified into a short period sensor, a long period sensor, and a broad band sensor according to a used frequency band. The short period sensor, which is a sensor designed for the purpose of observing a local micro-seismic tremor, has a flat region at a frequency of 1 Hz or more. Since the short period sensor has been designed for the purpose of a high frequency signal, it does not accurately sense a long distance micro-seismic tremor. On the other hand, the long period sensor shows a flat response in a low frequency band, such that it is appropriate for sensing a long distance seismic tremor, but has a difficulty in sensing a micro area seismic tremor generated in the vicinity. Since the broad band sensor, which uses a scheme of extending a band of a mechanical short period sensor up to a low frequency using a feedback circuit, may simultaneously record both of the micro area seismic tremor and the long distance seismic tremor, such that it may be appropriately used for studying a seismic tremor. The accelerometer, which is a sensor for sensing strong motion, provides important data in calculating an aseismic design parameter.
The micro-seismic sensor is classified into a ground surface micro-seismic sensor and an underground micro-seismic sensor according to an installation position thereof. Since the ground surface micro-seismic sensor is installed on a ground surface, it is directly affected by a surrounding environment, such that it may include a large amount of noise. On the other hand, the underground micro-seismic sensor is installed at a point at which it needs to be spatially installed even though an observation environment is not good, such that it may obtain good quality micro-seismic data. In the underground micro-seismic sensor, a scheme of first forming a borehole, temporarily fixing a micro-seismic sensor at a predetermined depth, and then permanently fixing the micro-seismic sensor by grouting is used. Therefore, once the micro-seismic sensor is installed, it may not be reused.